class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (head == nullptr) return nullptr;
        ListNode* cur = head;
        while (cur && cur->next) {
            if(cur->val == cur->next->val)
                cur->next = cur->next->next;
            else
                cur = cur->next;
        }
        return head;
    }
};